1. Field of the Invention
The present invention relates to a lambda-shaped carbazole and a main-chain NLO polyurethane containing the same.
2. Description of the Prior Art
Nonlinear Optical (NLO) materials can be categorized into two groups, i.e. organic and inorganic. Conventional inorganic NLO materials are LiNbO3 or GaAs crystals. Organic NLO materials, as described in Chemical Review vol. 94, No.1, 31-76(1994) published by American Chemical Society, have higher electro-optical coefficients than inorganic NLO materials. It is also reported that organic NLO materials possess characteristics of high optical coefficiency, short response time, and ease of processing (G. R. Meredith, et al, Macromolecules 1982, 15, 1385). Although organic NLO materials possess the superior characteristics described above, they have the disadvantages of inferior thermal stability, low temporal stability of polarized dipole and relatively high optical loss.
In fabrication of organic NLO materials, organic NLO chromophore is incorporated into polymeric materials by blending. One example of these organic NLO materials is guest-host type NLO material. Organic NLO materials can also be fabricated by incorporating organic NLO chromophore into polymeric materials through chemical bonding reaction. Example of these organic NLO materials are main-chain, side-chain or cross-linking NLO polymers.
In a main-chain NLO polymer, the dipole of a chromophore can be parallel to the main chain of a polymer to form head-to-tail main-chain NLO polymers (G. A. Lindsay et al. Macromolecules 1992, 25, 6075, and C. Wu et al. Macromolecules 1992, 25, 6716), or the dipole of a chromophore can be perpendicular to the main chain of a polymer to form shoulder-to-shoulder main-chain NLO polymer( N. Tsutsumi et al., Macromolecules 1996, 29, 592) and I. Teraoka et al. J. Appl. Phys. 1991, 69, 2568).
In head-to-tail main-chain NLO materials, the high driving voltage can cause significantly low effective order parameters, especially when the molecular weight is high enough to cause chain-entanglement; and the molecular structure thereof is more difficult to be ordered by electric field. This limits head-to-tail main-chain NLO polymers"" practical applications. In the shoulder-to-shoulder main-chain NLO materials, however, the aligning efficiency in electric field is raised because the dipole alignment of chromophores is perpendicular to the main chain of the polymer (Theory of Polymer Dynamics Oxford University Press: Oxford 1987xe2x80x9d, M. Doi and S. F. Edward). The solid stick-like structure increases the stability of the NLO coefficients of the materials at low temperatures. However, the solid stick-like structure also increases the local free volume between main chains of the material. The expanded local free volume may cause rapid relaxation when the temperature approaches the glass transition temperature of the material.
Accordingly, an ideal main-chain NLO material should possess both high poling efficiency in electric field and good thermal stability of NLO coefficients at high temperatures. However, in choosing polymeric materials for the main-chain NLO materials, some limitations should be considered, for example, polyacrylate and polymethacrylate have a glass transition temperature (Tg) of xe2x88x92105xc2x0 C., and thus are unstable under the actual application temperature. Polyimide, despite a high glass temperature when used in main-chain NLO materials, shows poor poling efficiency in electric field and low solubility. Accordingly, polyimide also has limited application in main-chain NLO materials. Polyurethane, however, thanks to ease of synthesis, good film-forming ability, and a glass transition temperature that can be modified by incorporating aromatic structure with different degrees of rigidity, has become an important base polymer of main-chain NLO materials ( S. S. H. Ma et al. (Chem. Mater. 1998, 10, 146).
In choosing NLO chromophores, two aspects should be considered. The first is whether the behavior of the chromophores per se, with respect to the NLO materials is stable after being incorporated into the polymers. For example, the size of the chromophores and the resonance length thereof will affect the alignment stability of dipole, the thermal stability of chromophores can be improved by increasing the resonance length, and the bulky structure can improve the volatility of the chromophores. Another aspect is the phase-matched phenomena of the NLO material. Generally, the phase-matched phenomena of the material can be improved by changing the structure of chromophores. However, conventionally, the phase match of second-order NLO coefficients is improved by adjusting the dielectric constant of materials. Recently, it has been found that the phase-matched phenomena can be improved by elevated off-diagonal components(i.e. d31, d32 . . . ). It has also been reported that carbazoles can be the base structures of the NLO chromophores because carbazoles possess a variety of electro-optical properties, such as photoconductivity ( B. Kippelen et al., J. Phys. Rev. B 1993, 48, 10710) and Y. Zhang et al., Appl. Phys. Lett. 1994, 66, 2561). It has also been disclosed that NLO chromophores with two-dimensional structure can be easily fabricated from carbazoles, because they possesses isoelectronic structure at 3rd and 6th positions (H. Yamamoto et al., Appl. Phys. Lett. 1992, 60, 935, X. T. Tao et al., Chem. Mater. 1995, 6, 1961, and X. T. Tao et al., J. Polym. Sci. B. Polym. Phys. 1995, 33, 2205). By using a two-dimensional carbazole, phase-matched second-harmonic coefficients can be significantly improved.
One object of the present invention is to provide a two-dimensional chromophore containing a lambda-shaped carbazole. The two-dimensional chromophore can increase the phase-matched second-harmonic coefficient.
Another object of the present invention is to provide a main-chain NLO polyurethane containing lambda-shaped chromophores.
The lambda-shaped carbazole has the following structure: 
wherein,
R1 and R2 are the same or different, independently selected from the group consisting of (xe2x80x94CH2xe2x80x94)n wherein n=2-11, (xe2x80x94CH2CH2Oxe2x80x94)m wherein m=1-4, phenylene and naphthalene;
R3 represents H(xe2x80x94CH2xe2x80x94)n wherein n=2-11 or H(xe2x80x94CH2CH2Oxe2x80x94)m wherein m=1-4.
Preferably, the n of (xe2x80x94CH2xe2x80x94)n is selected from n=2-6 and the m of (xe2x80x94CH2CH2Oxe2x80x94)m is selected from m=1-3.
Preferred lambda-shaped carbazoles include but are not limited to 9-hexyl-3,6-di(2-(6-hydroxyhexyl)sulfonylphenyl)-ethenyl)-9H-carbazole, 9-hexyl-3,6-di(2-(3-hydroxypropyl)sulfonylphenyl)-ethenyl)-9H-carbazole, 9-hexyl-3,6-di(2-(4-hydroxyphenyl)sulfonylphenyl)-ethenyl)-9H-carbazole, or 9-hexyl-3,6-di(2-(5-hydroxynaphthyl)sulfonylphenyl)-ethenyl)-9H-carbazole.
The above lambda-shaped carbazole chromophore can reduce the plasticization caused by chromophore to the main chain of a polymer material, and thus the temporal stability of the nonlinear optical coefficients is increased.
The following structure further illustrates the main-chain NLO polyurethanes containing the lambda-shaped carbazole of the invention. 
wherein,
R1 and R2 are the same or different, independently selected from the group consisting of (xe2x80x94CH2xe2x80x94)n wherein n=2-11, (xe2x80x94CH2CH2Oxe2x80x94)m wherein m=1-4, phenylene and naphthalene;
R3 represents H(xe2x80x94CH2xe2x80x94)n, wherein n=2-11 or H(xe2x80x94CH2CH2Oxe2x80x94)m wherein m=1-4.
Aromatic (Ar) diisocyanate moiety is derived from monomers selected from diisocyanate or the derivatives thereof.
Preferably, the n of (xe2x80x94CH2xe2x80x94)n is selected from n=2-6 and the m of (xe2x80x94CH2CH2Oxe2x80x94)m is selected from m=1-3. The diisocyanate derivatives include but are not limited to p-phenylene diisocyanate, 2,6-toluene diisocyanate, naphthalene-1,5-diisocyanate, methylene di(p-phenylene isocyanate), 2,2xe2x80x2-di(p-isocyanato phenylene)propane, 2,2xe2x80x2-di(p-isocyanato phenylene)hexafluoropropane, 3,3xe2x80x2-tolidene-4,4xe2x80x2diisocyanate, 3,3xe2x80x2-dimethoxy-4,4xe2x80x2-diisocyanato biphenyl, 2,2xe2x80x2-di(4-isocyanato phenoxy)biphenyl or isophorone diisocyanate.
Preferred main-chain NLO polyurethanes are the polymerization products of 9-hexyl-3,6-di(2-(3-hydroxypropyl)sulfonylphenyl)-ethenyl)-9H-carbazole and 2,2-di(p-isocyantophenylene)hexaflouropropane; 9-hexyl-3,6-di(2-(3-hydroxypropyl)sulfonylphenyl)-ethenyl)-9H-carbazole and 3,3xe2x80x2-dimethoxy-4,4xe2x80x2-diisocyanto biphenyl; or 9-hexyl-3,6-di(2-(3-hydroxypropyl)sulfonylphenyl)-ethenyl)-9H-carbazole and 2,2xe2x80x2-di(4-isocyanato phenoxy)biphenyl.
The main-chain NLO polyurethanes have a higher alignment stability in electric field because the dipole thereof is perpendicular to the main chain of the polymer, and thus the NLO coefficient is stabilized. The off-diagonal component d33 of the NLO materials is between 28-36, the d31 is between 8-12, and the d33/d31 ratio is about 3.
Hereinafter, the present invention will be described in more detail with reference to the Examples and drawings, however, it should be noted that the present invention is not limited to those Examples.